Powershell FTP Script Error: The remote server returned an error: 227 Entering Passive Mode

I am having Powershell FTP script problems. I have pulled my hair out over this one.

I recently setup an "automated build server" for my software projects. All software projects get built and bundled into a zip file. In theory, this zip file will be downloaded via FTP to several different servers. I am trying to build a powershell script that will download my package and unzip it into the desired directories.

The part I am having problem with is downloading the file via FTP. I am able to access the source file by manually logging into FTP via DOS command window. I can download the file just fine, so I know this is not a firewall issue. Atleast I dont think it is.

Whenever powershell starts to download the source .zip file, it hangs. I can see the file appear on the harddrive, but then disappears when the script fails. It never gets any bytes from the FTP server. I then receive this error:

Powershell FTP Script Error: The remote server returned an error: 227 Entering Passive Mode (10,255,130,77,231,5)
Blockquote

Here is my script:

#create destination directory (this is where the build files will be dropped)
[IO.Directory]::CreateDirectory("C:\tempftp")

"Creating staging folder..."
#create staging folder for deployment package bundle unzip
[IO.Directory]::CreateDirectory("C:\FINALDEPLOYMENTFOLDER")

#create destination and source paths for FTP copy command
$File = "C:\tempftp\MyPackageT.zip"
$ftp = "ftp://AdminiUser:adm1n1pwd@255.255.255.255/MyPackage.zip"

"ftp url: $ftp"

$webclient = New-Object System.Net.WebClient
$uri = New-Object System.Uri($ftp)

"Downloading $File..."

#perform the actual data transfer via FTP
$webclient.DownloadFile($ftp, $File)

"Unzip build package..."
#unzip the file that was transferred via FTP
$shell_app=new-object -com shell.application 
$zip_file = $shell_app.namespace("C:\tempftp\MyPackage.zip")         #source
$destination = $shell_app.namespace("C:\FINALDEPLOYMENTFOLDER")       #final destination

#unzip to destination folder
foreach ($item in $zip_file.Items())
{
$destination.CopyHere($item, 16)
}

I am able to run this script, locally, on my build server and it runs fine. I know this script works. My trouble is, why does this script barf on my non-build servers? Why is Passive Mode such a problem for this scenario and how do I fix it? Ive tried FTP IPv4 Address rules, FTP Firewall support changes, etc. But no success.

Noteworthy, I do see a warning message on my FTP Firewall Support section of IIS7.
It states:

To accept passive connections when you are using FTP over SSL (FTPS) or when your firewall does not filter packets, configure the external IPv4 address of your firewall.

^ I am unsure what that really means, but I will give it a shot. Any ideas why Passive Mode is such a pain in my neck? Should I not be using WebClient? I really want to avoid having to download another program/patch to make this work. Id rather this work in native Powershell…so no, I cant use FTP Client libraries!!

**** EDIT: I was able to fix this issue by opening "All Ports" on my firewall, but that seems a bit scary. Any suggestions on tracking down what ports are needed so that this Passive Mode error disappears? I already had a rule allowing a few specific ports I thought the FTP was using….but how can I see which ports I need to enable?**